There are two times that we read about the giving of the Torah: When we read Yisro and on Shavuos. On both days we read Haftoras of Neviyim going up to Shamayim. On Shavuos we read about Yechezkel ...
There seems to be a wide range of customs with regard to reading the haftara. In some shuls (mostly Chassidic) the one who is called up recites the berachah, and everyone then says the haftara quietly ...